1. Field of the Invention
The present invention is related to a coefficient of linear expansion measuring apparatus and coefficient of linear expansion measuring method where a coefficient of linear expansion of a sample is measured from an optical path length variation of reflected lights reflected on two reflection plates having a sample between them.
2. Description of Related Art
As for an apparatus for measuring a coefficient of linear expansion of a sample, what is called Fizeau interferometer and Michelson interferometer of double optical paths type can be given, where a sample is put between two reflector plates in the condition of tilting reflecting surfaces thereof each other slightly, a light having a known wavelength is irradiated from a single light source to each reflecting surface under vacuum, and an amount of expansion according to a temperature variation is measured by shift of interference fringes variation arisen by a interference of reflected lights (for example, see JIS R3251, appendix, 1995).
Many of the coefficient of linear expansion measuring techniques in earlier development have a constitution where shift of interference fringes and the variation thereof are observed and measured visually. Thus, it has been problematic that a user is under a large burden, and the possible deviation of test results depending on a user results less reproducibility.
In order to reduce a burden to a user, a measuring apparatus designed for automation is available in the market (ULVAC-RIKO, Inc.). However, imaging by an imaging member and image processing such as digitalization of the imaged data and the like are required for measuring and digitalizing shift of interference fringes variation. Thus, there have been problems such as complication of the equipment, decrease of the productivity and increase of the production cost thereof.